Make sleep threshold for delays configurable

This allows the minimum time that default_delay() will choose to sleep
for instead of polling to be configured at build-time. The default
remains unchanged at 100 milliseconds for now.

The test's correctness has been checked by testing with minimum sleep
time left at its default and set to a non-default value smaller than 100
microseconds (both pass without sleeping, verified with strace) and with
the minimum sleep time set to 0 (causing the test to be skipped). The
configured value from the macro needs to be stored in a const to avoid
-Werror=type-limits errors when configured to be zero.

Change-Id: Ida96e0816ac914ed69d6fd82ad90ebe89cdef1cc
Signed-off-by: Peter Marheine <pmarheine@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/81606
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>

meson_options.txt

@@ -22,3 +22,6 @@ option('man-pages', type : 'feature', value : 'auto', description : 'build the m
 option('documentation', type : 'feature', value : 'auto', description : 'build the html documentation')
 option('ni845x_search_path', type : 'string', value : 'C:\Program Files (x86)\National Instruments\Ni-845x\MS Visual C',
        description : 'Path to search for the proprietary ni845x library and header (32-bit Windows only)')
+option('delay_minimum_sleep_us', type : 'integer', min : 0, value : 100000,
+       description : 'Minimum time in microseconds to suspend execution for (rather than polling) when a delay is required.'
+                   + ' Larger values may perform better on machines with low timer resolution, at the cost of increased power.')